A wall-plug of the aforenoted type is used more particularly for fixing a heavy object to a support made from a hard material, after the wall-plug has been anchored within a hole previously bored within the material, the object then being disposed against the head of the shank and the edge of the anchorage hole.
The means permitting the relative movement of the shank and the socket, during and/or after expansion, makes possible, if the socket has been moved within its hole during expansion and therefore the shank with it, which frequently happens, a final movement of the shank, with respect to the socket which is then immobilized, for securing the object to be fixed firmly against the edge of the anchorage hole.
These same means also make it possible to overcome flatness deficiencies or thickness variations.
Such a wall-plug is already known from French patent FR-A-2 574 135.
In accordance with the wall-plug of this patent, the means allowing relative movement between the shank and the socket is formed by means of a shearable collar which is integral with the spacer which, after shearing following a predetermined force, allows the spacer to penetrate further into an intermediate ring integral with the socket.
The wall-plug of this patent has the drawback of being expensive to produce.
Still more particularly, document FR-A-2 291 400 teaches a cone expansion wall-plug comprising a shank with, at one end thereof, a truncated cone adapted for being driven in translation by means of the shank for causing expansion of an expansion zone of an expandable socket disposed about the shank, and means for securing the socket against translational movement during its expansion, the socket comprising an axially compressible zone whose internal diameter is equal to that of the expansion zone of the socket for permitting relative movement of the shank and the socket after expansion of the latter.
Because of the provision of the compressible zone of the socket there is no longer any need for provision of an intermediate ring.
The compressible zone of the socket provides a double function: by means of its compression, it makes possible a final movement of the shank with respect to the expansion zone of the socket, after expansion and immobilization thereof; and as a result of having the same internal diameter as that of the expansion zone, it participates with the latter in guiding the shank whose external diameter is substantially equal to the internal diameter of these two zones of the socket.
However, this last mentioned plug is not of simple and economic construction and the wedge effect defined between the cone and the socket is not perfect.